This invention relates to material handling equipment and in particular to the combination of a dock leveler and scissors lift combined into an operative system. In particular, this invention pertains to a unique manner in which those two components are combined to reduce the overall height of the system and provide support to the outboard end of the deck during a variety of operations. Such a reduction in overall height is an important advantage in terms of the dimensions of the pit in which the unit is to be mounted and the ability to service a variety of vehicles having different bed heights. Secondly, given that such devices accomplish dual modes of operation, one as a dock leveler and the second as a lifting table, support for the unit throughout all modes of travel including, below dock operation is a necessity. This invention thus relates to a combined system which permits the device to operate both as a lifting table and as a dock levelers incorporating the advantageous features of both.
The use of dock levelers at loading dock facilities is now well established. Those devices employ a deck which is generally hinged at one edge to a stationary frame mounted in a pit at the dock. The opposite or outboard end has a lip which is hingedly connected to an end of the deck. The deck is pivoted between an upwardly inclined position above the dock platform surface and a lower position which is below dock level. This ability to pivot both above and below the horizontal, cross-traffic, position allows the dock leveler to facilitate movement of goods to and from a vehicle irrespective of the height differential between the bed of the vehicle and that of the dock.
The lip, hinged to the front edge of the deck is movable from a pendant position to an extended position for purposes of bridging the gap between the rear edge of the bed of the vehicle and the front edge of the deck. Typical of such dock levelers are those found in U.S. Pat. Nos. 3,579,696, 3,669,601 and 3,728,753.
A second condition of dock loading occurs where material on the loading dock must be transferred to the roadway or vice-versa. Typically, in this situation a variety of devices have been used such as lift tables. These devices are essentially scissors lift platforms having a very low stored height yet, possess the ability to elevate and transfer heavy loads to a dock position. Some of these tables also incorporate a lip to act as a ramp for transfer between the table deck and the ground while in the lowered stored position. Typical are the scissors lift mechanisms found in U.S. Pat. Nos. 2,706,102, 2,928,558, 3,220,585, 3,246,876 and 3,259,369.
Efforts have been made to combine the features of dock levelers with those of lift tables into a combined unit. Typical is the subject matter disclosed in U.S. Pat. Nos. 4,995,103 and 5,111,546. Such devices tend to become very complex utilizing hydraulic and electronic controls and complicated mechanical elements for purposes of decoupling the rear hinge of the dock leveler deck for purposes of achieving an extended range of below dock operation. Also, in order to meet the strength requirements of the dock leveler, which operates in essentially a cantilever mode, these devices have large and complex frames.